How a quantum effect is gumming up nanomachines

By Saswato Das in New York city

HENRI LEZEC has a problem. He has been trying to use the tiny pressure exerted by light to move miniscule mechanical components. A light-powered micromachine could have all sorts of uses but Lezec, a photonics researcher at the US National Institute of Standards and Technology (NIST) in Gaithersburg, Maryland, hasn’t had much luck getting them to work. Frustratingly, the components keep sticking to the optical fibre that is beaming light at them.

Lezec is by no means alone in falling foul of what nanotechnologists call “stiction” – the collective term (derived from “static friction”) for a variety of physical forces that operate at the sub-micrometre scale. Stiction is a growing problem for engineers working with ever tinier devices because it gums up the works of microelectromechanical systems (MEMS) – which are increasingly used to make things like airbag sensors – and also affects computer hard drives and other devices with small moving parts.

“The unthinkable is beginning to happen,” says Federico Capasso, professor of applied physics at Harvard University. “Progress in micromachines and nanotechnology is slowing down because of quantum forces like the Casimir effect.”

This effect is a ghostly phenomenon whose properties remain poorly understood (see “Under pressure from quantum foam”). However, researchers reckon that the attractive force it creates is a major component of stiction at scales from 300 nanometres down to 10 nanometres. Capasso believes its influence is the reason that MEMS have not been miniaturised as quickly as computer chips – which have no moving parts – and it may block the development of even smaller nanoelectromechanical systems.

Small wonder, then, that dealing with the Casimir effect has become a

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